The present invention is directed to circuits for driving a plurality of stepping motor coils driven by driving impulses with both positive and negative (i.e. alternating) polarity, and in particular, to an improved circuit for driving a plurality of stepping motor coils with a minimal number of stepping motor coil drivers.
Wristworn timepieces such as chronograph watches, typically comprise a plurality of unidirectional or bi-directional stepping motors. One of the more popular types of stepping motors are the so-called “Lavet” type, and causing the rotation of the rotor in each of these stepping motors are one or more motor coils, as would be well known in the art. Exemplary unidirectional stepping motors are described in U.S. Pat. Nos. 4,550,279, 4,112,671 and 4,912,692 the disclosures of which are incorporated by reference as if fully set forth herein. Such stepping motors require only one motor coil, yet may be able to rotate in both a clockwise and counterclockwise direction. As would be understood in such examples, usually the driving impulse in the coil for a subsequent step in the same rotational direction as the previous step needs to be of an opposite polarity from the previous driving impulse for the previous step. In such a case, two motor coil drivers are needed to drive the one motor coil, where both of these drivers are forming a so-called “H-bridge” with the motor coil, wherein each of the motor coil's wires are connected to one of the two motor coil driver outputs.
On the other hand, a bi-directional stepping motor of the type described in co-pending U.S. patent application Ser. No. 10/090,588, the disclosure of which is also incorporated by reference as if fully set forth herein, requires two motor coils and reference should be made therein for an understanding of its applications and operation.
It has been recognized that advances in stepping motor driver circuitry are desirable. For example, state of the art devices, such as timepieces, having n motor coils, typically require 2n motor coil drivers if the stepping motors associated therewith need alternating driving impulse polarities. Consistent therewith, for each additional motor coil that is added to the particular device, two additional motor coil drivers would be necessary. Thus any additional stepping motors will tend to add more than an insubstantial amount of additional circuitry and power dissipation to a device. It would thus be desirable to reduce the number of needed motor coil drivers to drive a plurality of motor coils used in stepping motors driven devices.
The present invention achieves the foregoing and below mentioned objectives, as well as overcomes the perceived deficiencies in the prior art.